The idea of a colony of humans on Mars isn’t just science fiction anymore; NASA and space agencies around the world, along with independent scientists and researchers, are working hard to determine just what it would take for humanity to take root on the Red Planet. Getting there will be an immense challenge, as will setting up structures, creating sustainable sources of food, and battling the inhospitable elements, but sex might be the biggest risk of all.

In a new research paper published in Futures, an international team of scientists examines the challenges of reproduction on the Martian surface. It’s a risky proposition, but if humans succeed in conceiving, carrying, and birthing offspring on another world it might actually be the start of a new species.

In the paper, the researchers tackle a huge number of potential problems that could crop up when humans are finally ready to rear young on Mars. The first and most obvious hurdle is the low gravity environment, which could pose a serious threat to the conception and pregnancy processes that seem so simple here on Earth.

With just one-third the gravity of Earth, Mars travelers will be subjected to a whole range of health problems. Scientists know this because astronauts who have spent months and in some cases years in space have been closely studied for changes to their biology. Lower gravity causes muscles to deteriorate rapidly and can even weaken bone structure. On top of that, astronauts sometimes experience vision problems and even changes to the shape of their brains.

These are just the things that perfectly healthy adults have to deal with in space, which is to say nothing of the challenge of actually carrying a child in a microgravity environment. Put simply, we don’t even know if a human mother could carry a child to full term without something going wrong.

The paper also examines the inherent challenges of bolstering the numbers of a small colony of settlers on the planet. The concept of “love” might have to take a back seat to pure survival, with men and women being paired up by their biology rather than emotion. Additionally, some individuals may never be allowed to have children due to undesirable traits that are a risk to the colony as a whole.

In a somewhat scary aside, the researchers also note that editing the genes of future Mars babies might be an easy way to increase the prospects of survival. Pushing out bad traits and optimizing a human for life on Mars could give us a big edge, but as generations pass it would also result in a new kind of human — one who is fine on Mars but could never live a normal life here on Earth.